Nutrient extraction and recovery device for isolation and separation of target products from animal produced waste streams

ABSTRACT

The present invention provides for nutrient extraction and recovery devices that use the Donnan Membrane Principle (DMP) to cause spontaneous separation of dissolved ions along electrochemical potential gradients, wherein anions and cations such as H 2 PO 4   − , HPO 4   2− , PO 4   3− , Mg 2+ , Ca 2+ , NH 4   + , and K +  are moved from manure containing waste streams through cation and anion exchange membranes into a recovery stream thereby precipitating target compounds including but not limited to struvite, potassium struvite and hydroxyapatite.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/267,995 filed on Dec. 16, 2015, the contents of which areincorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

Field of Invention

The present invention relates generally to the problems associated withwaste in animal confinements, and more specifically, to separationmethods and systems for converting high concentrations of animal wastesinto nutrients and other useful products.

Related Art in Technical Field

The cleanup and handling of cattle, swine and poultry manure has becomea critical issue in the management and disposal of animal waste. Animalshave been raised for centuries for food and previously such animalsgrazed in fields or pens. Current methods of raising livestock includehousing in high concentration within a confined space. Numerousdrawbacks of such confinement include high concentrations of waste thatmust be removed from the confined space.

The manure produced must be removed regularly to ensure adequatesanitation and to prevent disease. One manure removal method is to floodthe housing area with water in order to wash away the manure. Theresulting effluent, that being a liquid/solid manure slurry, istypically directed through pipes or channels to a manmade slurry pond orlagoon, where the solids and particulates settle to the bottom and theanimal waste decomposes. After some decomposing, the waste can beapplied as a fertilizer. Additionally the liquid/solid manure can bedirected to a biodigester to capture some of the gaseous components ofthe manure and use the gases for energy, thereby reducing air qualityissues of manure accumulation and storage. However, the remainingliquids and solid from biodigestor processing must still be addressed tominimize loss of nutrient or contamination of lagoons, fields, drinkingwater, wells, or fresh water streams or lakes.

Notably, prolonged mixing of solid and liquid wastes in a waste manurelagoon can result in the transfer of a significant amount of nutrientsfrom the solid material to the surrounding liquid, so that the solidsbecome depleted of nutrients that may be desirable in a manurefertilizer. However, the liquids become loaded with nitrogen, phosphorusand salts to such an extent that they must be either limited in theirirrigation use, or mixed with fresh water to lower the proportion ofthese substances. In other words, the useful qualities of both the solidand liquid portions of the slurry mixture are degraded over time in aslurry pond or lagoon.

Further, the environmental impact can be substantial when applying thewaste to fields. Such environmental issues may include groundwaterleaching from the lagoon causing contamination of groundwater and/orstreams and sand soil contamination. Additionally, the high volume ofsolid waste manure, coupled with its use as fertilizer in local fields,results in increased levels of phosphorus, nitrogen, and potassium inthe soils. This may allow such chemicals to also leach into drainagewaters and run-off streams. The high volume of liquid waste manure,coupled with its use as fertilizer in local fields, results in increasedlevels of nitrogen rich ammonium and ammonia in the soils. This mayallow such chemicals to also leach into drainage waters and run-offstreams.

There has been increasing publicity and stricter environmentrequirements and enforcement because of the continuing concern overmaintaining water quality in watershed areas due to the release ofmanure as normal operational discharges from dairy cattle, beef cattle,swine, poultry and other concentrated animal feeding operations. Currenttechnologies for separating solids and nutrient components of suchanimal waste have limitations, are costly to operate, and result in theuse of large quantities of fuel and labor in order to provide solid andwater-based effluents that can either be recycled or are environmentallyacceptable to spread on farmlands.

Thus, what is needed is an improved process and separation system fortreating animal waste that is low in capital equipment cost, low inwaste transportation cost, prevents pollution of water resources, simpleto operate, and that provides solid and liquid effluents containingbeneficial and useful products to generate a sustainable supply ofnutrients critical for food production.

SUMMARY OF THE INVENTION

The present invention relates to separation systems and methods toprocess a manure source containing urine and fecal matter from cows,swine, sheep, goats, poultry, horses, rabbits and other animals toprovide target products including, but not limited to, ammonia,potassium, phosphorus, magnesium, struvite, potassium struvite,hydroxyapatite, nonpotable water and/or a filtrate with reduction ofresiduals for spraying on fields.

In one aspect, the present invention provides a process for treatingmanure in order to isolate a target precipitate, the process comprising:

a) providing a manure medium;b) introducing the manure medium into a separating system comprising:c) a waste compartment and a recovery compartment positioned within thewaste compartment, wherein the recovery compartment comprises at leastone cation exchange membrane and at least one anion exchange membrane,wherein the at least one cation exchange membrane and the at least oneanion exchange membrane are positioned on opposite or adjacent sides onthe recovery compartment, and wherein the recovery compartment comprisesan inlet and outlet for moving a recovery stream therethrough andwherein the recovery stream comprising an ionic solution comprisingsalts of Na⁺, K⁺, and/or NH₄ ⁺ with Cl⁻, HO⁻, HCO₃ ⁻, and/or HCOO⁻; andd) moving the manure medium into the waste compartment, wherein themanure medium contacts both the at least one cation exchange membraneand the at least one anion exchange membrane; wherein anions in thewaste medium will pass through the anion exchange membrane into therecovery stream and cations in the waste medium will pass through thecation exchange membrane into the recovery stream, wherein ions in therecovery stream form a precipitate selected from the group consisting ofstruvite, potassium struvite and/or hydroxyapatite. Preferrably, theinlet and outlet of the recovery compartment are positioned so that nomanure medium enters the recovery stream,

In another aspect, the present invention provides a process for treatingmanure in order to isolate at least one target precipitate, the processcomprising:

a) providing a manure medium;b) introducing the manure medium into a recovery system comprising:

-   -   a first and second waste compartment and a recovery compartment        positioned between the first and second waste compartments,        wherein the first and second waste compartments comprise an        inlet and outlet for moving a first and second waste stream        therethrough, respectively, wherein the recovery compartment        comprises an inlet and outlet for moving a recovery stream        therethrough, and wherein the first waste compartment is        separated from the recovery compartment by at least one cation        exchange membrane and the second waste compartment is separated        from the recovery compartment by at least one anion exchange        membrane;        c) separating the manure medium into the first and second waste        streams for introducing into the inlet of the first and second        waste compartments, respectively;        d) introducing an ionic solution comprising salts of Na⁺, K⁺,        and/or NH₄ ⁺ with Cl⁻, HO⁻, HCO₃ ⁻, and/or HCOO⁻ into the        recovery stream, wherein anions in the first waste stream will        pass through the at least one anion exchange membrane into the        recovery stream and cations in the second waste stream will pass        through the at least one cation exchange membrane into the        recovery stream, wherein a substantially equal amount of cations        and anions from the recovery stream will move into the        respective first and second waste stream, and wherein ions in        the recovery stream form a precipitate comprising struvite,        potassium struvite and/or hydroxyapatite thereby reestablishing        an electrochemical potential gradient across the at least one        cation and at least one anion exchange membranes to provide for        additional movement of ions through the anion and cation        exchange membranes thereby forming additional precipitate.

Preferably the waste stream comprises at least orthophosphate (alsowritten as P(V) (phosphorus in +5 oxidation state) or the H₃PO₄, H₂PO₄⁻, HPO₄ ²⁻, and PO₄ ³⁻ system), Mg²⁺, Ca²⁺, NH₄ ⁺ and K⁺ ions that moveinto the recovery stream thereby precipitating as the compoundsstruvite, potassium struvite or hydroxyapatite. As the struvite,potassium struvite or hydroxyapatite minerals are formed they can beremoved from the recovery stream, by known separation means. The wastestreams and the recovery stream can be recirculating to provideadditional access to the cation and anion exchange membranes.

Notably, struvite, potassium struvite and hydroxyapatite are all solublein an aqueous solution when the pH is less than about 5.0. The dominantphosphate species is HPO₄ ²⁻ at pH of about 7.5 and as the pH increasesmore HPO₄ ²⁻ is available to form more nutrient-rich minerals. The idealpH for the formation of nutrient-rich minerals is from about 7.0 to11.0. Thus, the recovery stream can operate in the near-neutral oralkaline pH range to ensure maximal formation of nutrient-rich minerals.

At stated above, the manure medium contains at least phosphorus andnitrogenous compounds and in some situations the addition of magnesiumchloride (MgCl₂) to the recovery compartment or the waste compartmentmay be necessary to force the precipitation of struvite (MgNH₄PO₄.6H₂O).Further, adjusting the pH of the solution in the recovery chamber to apH of about 9.0-10 with sodium hydroxide (NaOH) can increase formationof potassium struvite. Additionally, the present invention has theability to provide for the formation of hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). To proceed with the formation of hydroxyapatite, acalcium source may be added into the waste streams and phosphorus isrecovered in the form of calcium phosphate.

The precipitated nutrient-rich minerals can be utilized as a slowrelease fertilizer as either as a specialty fertilizer in plantnurseries or blended into main agricultural fertilizers. Notably, evenwhen applied at relatively high application rates, struvite can act as aslow release fertilizer without damaging plant roots and leachingpotential is low. The process can be controlled to generatepredominantly struvite, potassium struvite, or hydroxyapatite. By mixingthese products, custom fertilizers with specific nitrogen to phosphorusto potassium (NPK) ratios can be generated.

In another aspect, the present invention provides for a system forprecipitating struvite, potassium struvite and or hydroxyapatite, thesystem comprising:

-   -   a waste compartment and a recovery compartment positioned within        the waste compartment, wherein the recovery compartment        comprises at least one cation exchange membrane and at least one        anion exchange membrane, wherein the at least one cation        exchange membrane and the at least one anion exchange membrane        are positioned on opposite or adjacent sides on the recovery        compartment, and wherein the recovery compartment comprises an        inlet and outlet for moving a recovery stream therethrough and        wherein the recovery stream comprising an ionic solution        comprising salts of Na⁺, K⁺, and/or NH₄ ⁺ with Cl⁻, HO⁻, HCO₃ ⁻,        and/or HCOO⁻.

In yet another aspect, the present invention provides for a system forisolating and precipitating struvite, the system comprising:

-   -   a first and second waste compartment and a recovery compartment        positioned between the first and second waste compartments,        wherein the first and second waste compartments comprise an        inlet and outlet for moving a first and second waste stream        therethrough, respectively, wherein the recovery compartment        comprises an inlet and outlet for moving a recovery stream        therethrough, and wherein the first waste compartment is        separated from the recovery compartment by at least one cation        exchange membrane and the second waste compartment is separated        from the recovery compartment by at least one anion exchange        membrane.

Livestock manure besides containing a mixture of feces and urine mayalso include wasted feed, bedding and water (including: spilled water,flush water, wash water, and precipitation). Manure characteristics aregenerally affected by diet, species and the growth stage of the animals,and the manure collection method used, including the amount of wateradded to dilute the waste. Typically, animal waste manure is about 80%to about 95% liquid by weight due to urine, sloppy drinking, animalwashing and flush water. As such, the manure medium may be pretreatedwith mechanical system to remove any unwanted material, larger solidsand excess liquids from the manure medium before introduction into thesystem of the present invention, wherein the pretreating includessystems such as screw press, centrifuge, vibrating screen, meshscreening, belt filter, hydrocylcone and other systems that may furtherreduce particle size, and/or remove unwanted large material to ensureeasy flow through the first and second waste streams.

Further, the manure may be pretreated in an anaerobic digester, whichincludes holding manure in an air-tight tank that is heated to about 100degrees. Bacteria in the manure thrive in these conditions and theyconsume solids in the manure while releasing methane gas. Naturallyoccurring bacteria will degrade the volatile solids, releasing acombination of carbon dioxide (CO₂) and methane (CH₄) that may beburned/combusted for energy production. Digestion does not reduce thenutrients in the manure, although it may alter the form of the nitrogen(more ammonia) and phosphorus (more orthophosphate).

Notably, ferric chloride (FeCl₃), ferric sulfate (FeSO₄), calciumhydroxide (lime), aluminum sulfate (alum) and aluminum chloride (AlCl₃)can also be used for phosphorus binding and the formation of commonphosphorus salts. The addition of these binding agents forms a solidsalt that can be collected and removed by filtration.

Still further, the manure medium may be treated with chemicals to helpseparate solids from liquids. Flocculation is a process that convertscoagulated particles into large, rapidly settling masses, also calledflocs. The most common chemicals used to coagulate and flocculate solidsin animal manure and wastewater are organic polymers such aspolyacrylamide (PAM), and metal salts such as ferric chloride (FeCl₃),alum (Al₂(SO₄)₃) and lime (Ca(OH)₂). Such flocs can be further removedby screening methods or centrifuging.

The recovery stream, with the removal of salt content, may be utilizedas the liquid fertilizer and the treated waste stream may be dehydratedto minimize water content and provides for a solid fertilizer.

In yet another aspect, the present invention provides for a method toisolate struvite, potassium struvite and hydroxyapatite from a manuremedium, the method comprising:

a) providing a manure medium comprising P(V), Mg²⁺, Ca²⁺, NH₄ ⁺, and K⁺ions;b) introducing the manure medium into a recovery system comprising:

-   -   a first and second waste compartment and a recovery compartment        positioned between the first and second waste compartments,        wherein the first and second waste compartments comprise an        inlet and outlet for moving a first and second waste stream        therethrough, respectively, wherein the recovery compartment        comprises an inlet and outlet for moving a recovery stream        therethrough and wherein the first waste compartment is        separated from the recovery compartment by at least one cation        exchange membrane and the second waste compartment is separated        from the recovery compartment by at least one anion exchange        membrane;        c) separating the manure medium into the first and second waste        streams for introducing into the inlet of the first and second        waste compartments, respectively;        d) introducing a ionic solution comprising salts of Na⁺ or, K⁺        with Cl⁻, HO⁻, HCO₃ ⁻, and/or HCOO⁻ into the recovery stream,        wherein the HPO₄ ²⁻ anions in the first waste stream will pass        through the at least one anion exchange membrane into the        recovery stream and Mg²⁺ and NH₄ ⁺ cations in the second waste        stream will pass through the at least one cation exchange        membrane into the recovery stream, wherein a substantially equal        amount of Na⁺ cations and Cl⁻ anions from the recovery stream        will move into the respective first and second waste stream, and        wherein ions in the recovery stream form a struvite precipitate        thereby reestablishing an electrochemical potential gradient        across the cation and anion exchange membranes to provide for        additional movement of ions through the anion and cation        exchange membranes.

In a still further aspect, the present invention provides for a methodto isolate struvite, potassium struvite and hydroxyapatite from a manuremedium, the method comprising:

a) providing a manure medium comprising P(V), Mg²⁺, Ca²⁺, NH₄ ⁺, and K⁺ions;b) introducing the manure medium into a recovery system comprising:

-   -   a waste compartment and a recovery compartment positioned within        the waste compartment, wherein the recovery compartment        comprises at least one cation exchange membrane and at least one        anion exchange membrane, wherein the at least one cation        exchange membrane and the at least one anion exchange membrane        are positioned on opposite or adjacent sides on the recovery        compartment, and wherein the recovery compartment comprises an        inlet and outlet for moving a recovery stream therethrough;        c) moving the manure medium into the waste compartment, wherein        the manure medium contacts both the at least one cation exchange        membrane and the at least one anion exchange membrane; and        d) introducing a ionic solution comprising salts of Na⁺ or, K⁺        with Cl⁻, HO⁻, HCO₃ ⁻, and/or HCOO⁻ into the recovery stream,        wherein the HPO₄ ² anions in the manure medium will pass through        the at least one anion exchange membrane into the recovery        stream and Mg²⁺ and NH₄ ⁺ cations in the manure medium will pass        through the at least one cation exchange membrane into the        recovery stream, wherein a substantially equal amount of Na⁺        cations and Cl⁻ anions from the recovery stream will move into        manure medium, and wherein ions in the recovery stream form a        struvite, potassium struvite or hydroxyapatite precipitate        thereby reestablishing an electrochemical potential gradient        across the at least one cation and at least one anion exchange        membrane to provide for additional movement of ions through the        at least one anion and the at least one cation exchange        membranes.

Other aspects and advantages of the invention will be more fullyapparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows Simultaneous recovery of nutrient-rich solutions that canbe used to precipitate struvite-based solids using a three-chamberdesign that incorporates both anion and cation exchange membranes. Notethat the two waste chambers are one container, and the secondcompartment is essentially an insert containing an anion exchangemembrane on one side, and a cation exchange membrane on the other. Thissetup ensures that changes to the chemistry of the first chamber arereflected in the third chamber. (a) initial conditions with wastecompartments and a NaCl-based draw solution; (b) transport of anions andcations across the anion and cation exchange membranes, respectively;(c) equilibrium situation with selective recovery of PO₄ ³⁻ (as HPO₄ ²⁻here), Mg²+, and NH₄ ⁺, which precipitate to form struvite.

FIG. 2 shows (a) phosphorus and (b) magnesium/ammonium recovery usingthe Donnan Membrane Principle with anion and cation exchange membranes.Note that solid particles and cations cannot cross the anion exchangemembrane and anions cannot cross the cation exchange membrane andelectronneutrality is maintained.

FIG. 3 shows and illustration of the impact of the Donnan MembranePrinciple for nutrient recovery.

FIG. 4 shows a schematic representation of a chamber-type nutrientextraction and recovery device (NERD) wherein the recovery compartmentis included in a waste compartment (not shown).

FIG. 5 shows an alternative system for recovery of nutrients from wastematerial.

FIG. 6 is a photograph of laboratory-scale DMP-based NERD reactorcontaining (left) poultry litter extract and (right) NaCl draw solution.

FIG. 7 shows the recovery of >99% phosphorus from a synthetic wastewaterusing a NaCl draw solution.

FIG. 8 shows the recovery of >99% phosphorus from synthetic wastewaterusing an NaOH-based draw solution.

FIG. 9 shows data demonstrating the use of a regular precipitationscheme to maintain the electrochemical potential gradient for long-termphosphorus recovery.

FIG. 10 shows SEM microphotographs of (a-b) struvite and (c-d) potassiumstruvite recovered from NERD reactors treating synthetic wastewater.

FIG. 11 shows recovery of P(V) from a slurry containing 1 g/L of poultrylitter using a draw solution of 10 g/L NaCl.

DETAILED DESCRIPTION OF THE INVENTION

Nutrient extraction and recovery devices (NERDs) exploit the DonnanMembrane Principle (DMP) [1-4] to cause spontaneous separation ofdissolved ions along electrochemical potential gradients. Thisinnovative technology challenges conventional wisdom by taking acompletely different approach to nutrient recovery. Given the highenergy and chemical costs associated with traditional approaches, thepresent invention provides for a novel and effective extraction system.

The invention takes advantage of the DMP for removal and recovery ofP(V) (as HPO₄ ²⁻ here), Mg²⁺, Ca²⁺, NH₄ ⁺, and K⁺ ions from waste sludgesuch as manure. The Donnan membrane principle is based on the Donnanco-ion exclusion phenomenon, according to which negatively chargedcation exchange membranes will reject anions, while positively chargedanion exchange membranes will reject cations. Unlike other membraneprocesses, the Donnan membrane principle does not require a pressuregradient or an electric current supply, and operates by virtue of theelectrochemical potential difference between electrolytes on two sidesof an ion exchange membrane.

The term “manure” refers to any medium that includes animal waste andmay also include but is not limited to water, feed, urine, fecal matter,straw, hay, bedding material, peat moss, and composts.

The system and individual compartments may be fabricated from anymaterial that does not interact with any ions in the waste or recoverystreams, including but not limited to polymeric, metallic or ceramicmaterial.

In some embodiments, the cation exchange membranes, as disclosed herein,are conventional and are available from, for example, Asahi Kasei ofTokyo, Japan; or from Membranes International of Glen Rock, N.J., orDuPont, in the USA or SELEMION® by AGC Engineering Co., Ltd., Examplesof cation exchange membranes include, but are not limited to, N2030WX(Dupont), F8020/F8080 (Flemion), FKE (Fuma Tech), CMI-7000 (MembranesInternational, Nafion 117 (Dupont) and F6801 (Aciplex). Cation exchangemembranes that are desirable in the methods and systems of the inventionhave minimal resistance loss, greater than 90% selectivity, and highstability in concentrated caustic. Examples of cationic exchangemembranes include, but not limited to, cationic membrane consisting of apolymer containing anionic groups, for example sulfonic and/orcarboxylic groups. However, it may be appreciated that in someembodiments, depending on the need to restrict or allow migration of aspecific cation or an anion species between the electrolytes, a cationexchange membrane that is more restrictive and thus allows migration ofone species of cations while restricting the migration of anotherspecies of cations may be used.

Anion exchange membranes allow passage of salt ion such as chloride ionto the waste stream. Preferably the anion exchange membrane is alsosubstantially resistant to the organic compounds such that the anionexchange membranes does not interact with the organics. For exampleonly, polymers containing fixed tertiary or quaternary ammonium groupsmay be used as anion exchange membranes. Similarly, depending on theneed to restrict or allow migration of a specific anion species, ananion exchange membrane that is more restrictive and thus allowsmigration of one species of anions while restricting the migration ofanother species of anions may be used. Examples of anion exchangemembranes include, but are not limited to, FAA-3 (Fuma Tech), AMI-7001(Membranes International) and AMX (Astom).

In some embodiments, the membranes used in the methods and systemsprovided herein are ion exchange membranes reinforced with a materialfor reinforcement and are of a certain thickness. For example, in someembodiments, the thickness of the membrane is between 20-130 um; orbetween 20-110 um; or between 20-110 um; or between 20-80 um; or between20-75 um; or between 20-60 um; or between 20-50 um; or between 20-40 um;or between 20-35 um. In some embodiments, the membrane may be reinforcedwith materials such as, but not limited to, polymers, such as,polyethylene (PET), polypropylene (PP), and polyether ether ketone (PK),and glass fiber (GF).

The present invention works by exploiting DMP, which driveselectrochemical potential equilibrium between two solutions separated byan ion exchange membrane, to recover nutrients. In particular, arecovery or draw solution containing less preferred species (e.g., Cl⁻)facilitates exponential recovery of more preferred species, such as PO₄³⁻ and valuable cationic species (e.g., NH₄ ⁺, Mg²⁺, Ca²⁺) can also berecovered. In tandem, the selectively separated nutrients facilitaterecovery of value-added products, such as struvite, potassium struviteand hydroxyapatite.

Phosphorus and other nutrients can be selectively extracted from animalmanure and concentrated in high-purity solutions. The chemicalconditions in the recovery solution cause precipitation of valuablefertilizers. The present system does not require chemical addition orelectricity; furthermore, this technology can be directly incorporatedinto manure pits and lagoons.

Current technologies rely on effective separation of nutrients before aforced chemical precipitation. For instance, previous researchers haveused hybrid ion exchange resins and modified clay sorbents toeffectively isolate phosphate (PO₄ ³⁻) and/or ammonium (NH₄ ⁺);following separation, nutrients are eluted from the sorbent media, mixedwith MgCl₂, and recovered as struvite [5-8]. The present invention doesnot require energy intensive processes or external chemical addition.

The process works by exploiting electrochemical potential equilibriumbetween two solutions separated by an ion exchange membrane. Forsimplicity, the two chambers will be labeled as waste (that containingmanure from animal, such as poultry) and recovery (the draw solution) asshown in FIG. 1. To highlight the fundamentals of the proposed process,consider FIG. 2a , which illustrates P(V) recovery. The waste chambercontains wastewater, waste activated sludge, or agricultural waste andthe recovery chamber contains a draw solution composed of high-strengthsodium chloride. While the process looks similar to an electrodialysiscell, no electricity is used here. Instead, the differences inelectrochemical potential between the waste and draw solutions drivesthe system to thermodynamic equilibrium by exchanging ions.

At equilibrium,

μ _(P(V)) ^(waste)=μ _(P(V)) ^(recovery)  (Eq. 1)

where, μ is the electrochemical potential, waste designates the chambercontaining a poultry litter slurry, and recovery designates the chamberin which P(V) (i.e., the H₃PO₄, H₂PO₄ ⁻, HPO₄ ²⁻, and PO₄ ³⁻ system) isrecovered. Eq. 1 can be expanded to Eq. 2.

μ_(P(V)) °+RT ln a _(P(V)) ^(waste) +zFφ ^(waste)=μ_(P(V)) °+RT ln a_(P(V)) ^(recovery) +zFφ ^(recovery)  (Eq. 2)

In Eq. 2, μ° is the electrochemical potential at standard conditions, Ris the gas constant, T is temperature, a is activity, z is the charge ofthe diffusing ion, F is the Faraday constant, and φ is the electricalpotential. Rearranging Eq. 2 yields Eq. 3.

$\begin{matrix}{\frac{F\left( {\varphi^{waste} - \varphi^{recovery}} \right)}{RT} = {{\ln \left( \frac{a_{P{(V)}}^{recovery}}{a_{P{(V)}}^{waste}} \right)}^{\frac{1}{z_{P{(V)}}}} = {\ln \left( \frac{a_{draw}^{recovery}}{a_{draw}^{waste}} \right)}^{\frac{1}{z_{draw}}}}} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

The second part of Eq. 3 is solved for a generic species, labeled drawhere to refer to a draw ion present in the recovery solution. If theactivity corrections for P(V) and the draw ion are similar on eitherside of the ion exchange membrane, Eq. 3 can be collapsed to Eq. 4,where C is molar concentration.

$\begin{matrix}{\left( \frac{C_{P{(V)}}^{recovery}}{C_{P{(V)}}^{waste}} \right)^{z_{draw}} = \left( \frac{C_{draw}^{recovery}}{C_{draw}^{waste}} \right)^{z_{P{(V)}}}} & \left( {{Eq}.\mspace{14mu} 4} \right)\end{matrix}$

If HPO₄ ²⁻ is being exchanged with Cl⁻ (or any other monovalent ion),then Eq. 5 describes the corresponding equilibrium ratios in therecovery and waste compartments.

$\begin{matrix}{\frac{\left\lbrack {HPO}_{4}^{2 -} \right\rbrack^{recovery}}{\left\lbrack {HPO}_{4}^{2 -} \right\rbrack^{waste}} = \left( \frac{\left\lbrack {Cl}^{-} \right\rbrack^{recovery}}{\left\lbrack {Cl}^{-} \right\rbrack^{waste}} \right)^{2}} & \left( {{Eq}.\mspace{14mu} 5} \right)\end{matrix}$

Therefore, by maintaining a molar ratio of [Cl⁻]^(recovery) to[Cl⁻]^(waste) of 10, the concentration of HPO₄ ²⁻ in the recovery sideof the reactor should be approximately 100× that in the waste chamber.In practice, this means that 99% of phosphorus can be recovered into a“clean” solution. Since solids and cations cannot cross the anionexchange membrane, the recovery solution contains phosphorus, the drawion (Cl⁻ in this example), and the co-ion added with Cl⁻ (e.g., Na⁺, ifNaCl was used to generate the draw solution).

A similar scheme using a cation exchange membrane can recover Mg²⁺,Ca²⁺, NH₄ ⁺, and K⁺ (FIG. 2b ). These cations are important for recoveryof struvite, potassium struvite and hydroxyapatite solids. Bymaintaining a molar ratio of [Na⁺]^(recovery) to [Na⁺]^(waste) of 10,the Mg²⁺, Ca²⁺, NH₄ ⁺, and K⁺ recovery efficiencies would be 99%, 99%,90%, and 90%, respectively. Since dissolved NH₄ ⁺ and K⁺ levels aretypically greater than P(V) concentrations, the lower recovery of thesespecies does not affect our ability to precipitate struvite-likeminerals. The concentration effect observed during the Donnan MembranePrinciple is illustrated in FIG. 3.

These two streams, namely the P(V) and Mg—NH₄—K rich solutions, can bemixed at the proper ratio to produce struvite or potassium struvite. Themixing ratio will be dependent on the total phosphorus concentration inthe recovery solution from FIG. 2a and the magnesium andammonium/potassium concentrations in the recovery solution from FIG. 2b. The dissolution reactions (Rxns. 1-2) and equilibrium constants (Eq.7-8) for struvite and potassium struvite are shown below, respectively.

MgNH₄PO₄.6H₂O(s)⇄Mg²⁺+NH₄ ⁺+PO₄ ³⁻+6H₂O  (Rxn. 1)

K_(sp.NH) ₄ _(MgPO) ₄ _(.6H) ₂ _(O)=10^(−13.3)=[NH₄ ⁺][Mg²⁺][PO₄³⁻]  (Eq. 6)

MgKPO₄.6H₂O(s)⇄Mg²⁺+K⁺+PO₄ ³⁻+6H₂O  (Rxn. 2)

K_(sp.KMgPO) ₄ _(.6H2O)=10^(−10.6)=[K⁺][Mg²⁺][PO₄ ³⁻]  (Eq. 7)

The nutrient extraction technology of the present invention can bedeveloped into a suite of commercial products aimed at providing on-sitenutrient recovery. These products include chamber-, tubular-, andenvelope-type systems. The chamber- and tubular-nutrient extractiondevices of the present invention are expected to be most relevant to onsite nutrient recovery from animal manure pits and lagoons. Thesedevices can be easily assembled into a manifold that can be lowered intopits/lagoons and lifted for cleaning purposes. Operational units willinvolve a continuous flow of draw solution to allow collection ofprecipitated fertilizer products. In that case, nutrient extractionsystems will contain a separate gravimetric separation that allowscollection of solids and recirculation of bulk draw solutions.

The chamber-type devices can be constructed of PVC piping. Cation(CM1-7000) and anion (AMI-7001) exchange membranes from MembranesInternational Inc. (Ringwood, N.J.) may be employed. Salient propertiesof the ion exchange membranes are provided in Table 1.

TABLE 1 Salient information for the ion exchange membranes ParameterCMI-7000 AMI-7001 Functionality Strong Acid Strong base Polymerstructure Gel polystyrene Gel polystyrene Cross-linking DivinylbenzeneDivinylbenzene Functional group Sulfonic acid Quaternary ammonium Parentform Sodium Chloride Thickness (mm) 0.45 ± 0.25 0.45 ± 0.25 Capacity(meq/g) 1.6 ± 0.1 1.3 ± 0.1 Water permeability <3 <3 (mL/hr-ft² at 5psi) Chemical stability range (pH) 1-10 1-10

A generalized schematic of the chamber-type passive sampling devices isprovided in FIG. 4. The main section of the proposed device is athree-way-tee piece of PVC piping; this piping has one outlet on thez-axis and two outlets along the x-axis. The outlet on the z-axis isfitted with a male adaptor to allow for capping; therefore, this outletrepresents the filling/emptying port for the device. The cap is fittedwith a rubber septum to allow for easy sampling. The two side outlets(along the x-axis) are fitted with PVC flanges; corresponding pieces ofPVC pipe are also fitted with PVC flanges. Cross-sections of cation andanion exchange membranes are fitted between these pieces as indicated inFIG. 4. Flanges may be secured using stainless steel screws, washers,and nuts.

A prototype reactor with 2-L waste and recovery chambers separated by ananion exchange membrane (FIG. 6). For all preliminary experimentation, aAMI-7001 (Membranes International) was used which is a strong base anionexchange membrane consisting of a gel polystyrene polymer cross-linkedwith divinylbenzene and quaternary ammonium functional groups (totalexchange capacity=1.3 meq/g). Preliminary experimentation was conductedfor P(V) recovery from synthetic wastewater, wastewater effluent, andanimal manure. The reactor body was constructed using clearpolycarbonate, silicon frames (to prevent water leakage around themembrane), and stainless steel screws, washers, and nuts. The reactorchambers were continuously mixed using magnetic stirrers.

Optimization of Nutrient Recovery Efficiency and Kinetics

Results from an experiment with synthetic wastewater are shown in FIG.7. The synthetic wastewater was comprised of 100 mg/L of Na₂HPO₄ (pH,9.8; conductivity, 113 μS/cm), while the draw solution contained 10 g/LNaCl (pH, 6.22; conductivity, 18.1 mS/cm). Phosphorus in the wastecompartment rapidly exchanged with chloride from the recoverycompartment in the first eight hours of operation. After 24 hours,almost all of the phosphorus was recovered. For this scenario, themaximal chloride transfer is equivalent to two times the initial HPO₄ ²⁻concentration. The corresponding chloride ratio in the waste/recoverychambers will be as high as 120 mol/mol. Then, the P(V) recovery will beas high as 99.99%.

A similar experiment was run using a synthetic wastewater containing of100 mg/L of Na₂HPO₄ (pH, 9.8; conductivity, 113 μS/cm), while the drawsolution contained 100 mM NaOH (pH, 12.7; conductivity, 22.7 mS/cm). TheP(V) recovery was >99%, as indicated in FIG. 8.

Selective Recovery of Struvite-Based Minerals

Using the reactor in FIG. 6, experiments were conducted to investigatethe selective and continuous recovery of struvite minerals. FIG. 9 showsdata from an experiment with a 100 mg/L Na₃PO₄ synthetic wastewater (pH,10.4; conductivity, 135 μS/cm) with a 10 g/L NaCl draw solution (pH,6.2; conductivity, 18.1 mS/cm). Over the first 24 hours of operation,P(V) was effectively recovered in the draw solution. At 24 hours, wedosed another 100 mg/L of Na₃PO₄ into the waste chamber andsimultaneously added MgCl₂ and NH₄Cl into the recovery chamber inequimolar fashion to the recovered P(V). These treatments caused theP(V) concentration to increase in the waste compartment and decrease inthe recovery chamber due to struvite precipitation. In combination,these changes also re-established the electrochemical potential gradientacross the anion exchange membrane, resulting in continued recovery from24 to 48 hours. At 48 hours, over 95% P(V) recovery was achieved.

P(V) was recovered using draw solutions containing MgCl₂ and NH₄Cl orKCl. Because the Mg²⁺ and NH₄ ⁺ or K⁺ were present in the recoverycompartment in excess of P(V), the recovered phosphorus was driventowards precipitation as struvite or potassium struvite. Scanningelectron microscopy (SEM) microphotographs of the recovered solids areshown in FIG. 10. The particles in FIG. 10 (a-b) were recovered using adraw solution with MgCl₂/NH₄Cl, whereas the images in FIG. 10 (c-d) stemfrom an experiment with a MgCl₂/KCl draw solution. Note thatenergy-dispersive X-ray spectroscopy (EDS) analyses confirmed mineralcomposition. From the SEM images, the morphological differences betweenstruvite and potassium struvite are clear, with “needle-like” struvitecrystals and “flake-like” potassium struvite precipitates.

Nutrient Recovery from Wastewater, Activated Sludge, & Animal Manure

A study was conducted to recover phosphorus from a poultry litter slurry(FIG. 11). After 38 hours, over 70% of the P(V) was recovered. While therate of recovery was slower than the synthetic solutions describedabove, the extent of recovery indicates that the overall recoverypotential is still high. Furthermore, the AMI-7001 membranes that wereused in this experiment were relatively thick, 450±25 um. Notably thethickness of the ion exchange membranes may be thinner (i.e., 200 um orless), and should provide faster recovery rates in real wastewaters.

REFERENCES

The contents of all references cited herein are incorporated byreference herein for all purposes.

-   1. Sarkar, S., SenGupta, A. K., Prakash, P. (2010). The Donnan    Membrane Principle: Opportunities for Sustainable Engineered    Processes and Materials. Environmental Science & Technology 44(4),    1161-1166.-   2. Prakash, P., SenGupta, A. K. (2005). Modeling A13+/H+ ion    transport in Donnan membrane process for coagulant recovery. AlChE    Journal 51(1), 333-344.-   3. Prakash, P., Hoskins, D., SenGupta, A. K. (2004). Application of    homogeneous and heterogeneous cation-exchange membranes in coagulant    recovery from water treatment plant residuals using Dorman membrane    process. Journal of Membrane Science 237(12), 131-144.-   4. Prakash, P., SenGupta, A. K. (2003). Selective Coagulant Recovery    from Water Treatment Plant Residuals Using Dorman Membrane Process.    Environmental Science & Technology 37(19), 4468-4474.-   5. O'Neal, J. A., Boyer, T. H. (2013). Phosphate recovery using    hybrid anion exchange: Applications to source-separated urine and    combined wastewater streams. Water Research 47(14), 5003-5017.-   6. Sendrowski, A., Boyer, T. H. (2013). Phosphate removal from urine    using hybrid anion exchange resin. Desalination 322, 104-112.-   7. Karunanithi, R., Szogi, A. A., Bolan, N., Naidu, R., Loganathan,    P., Hunt, P. G., Vanotti, M. B., Saint, C. P., Ok, Y. S.,    Krishnamoorthy, S. (2015). Phosphorus recovery and reuse from waste    streams. Adv. Agron 131.-   8. Sengupta, S., Nawaz, T., Beaudry, J. (2015). Nitrogen and    Phosphorus Recovery from Wastewater. Current Pollution Reports,    1-12.

That which is claimed is:
 1. A process for treating manure in order toisolate a target precipitate, the process comprising: a) providing amanure medium; b) introducing the manure medium into a separating systemcomprising: a waste compartment and a recovery compartment positionedwithin the waste compartment, wherein the recovery compartment comprisesat least one cation exchange membrane and at least one anion exchangemembrane, wherein the at least one cation exchange membrane and the atleast one anion exchange membrane are positioned on opposite or adjacentsides on the recovery compartment, and wherein the recovery compartmentcomprises an inlet and outlet for moving a recovery stream therethrough,and wherein the recovery stream comprising an ionic solution comprisingsalts of Na⁺, K⁺, and/or NH₄ ⁺ with Cl⁻, HO⁻, HCO₃ ⁻, and/or HCOO⁻; andc) moving the manure medium into the waste compartment, wherein themanure medium contacts both the at least one cation exchange membraneand the at least one anion exchange membrane, wherein anions in themanure medium will pass through the anion exchange membrane into therecovery stream and cations in the manure medium will pass through thecation exchange membrane into the recovery stream, wherein ions in therecovery stream form a precipitate.
 2. The process of claim 1, whereinthe manure medium comprises H₃PO₄, H₂PO₄ ⁻, HPO₄ ²⁻, and/or PO₄ ³⁻, Ca²⁺or Mg²⁺, NH₄ ⁺ or K⁺ ions.
 3. The process of claim 1, wherein theprecipitate is struvite, potassium struvite, or hydroxyapatite.
 4. Theprocess of claim 1, wherein the recovery stream has a pH ranging fromabout 7 to
 11. 5. The process of claim 3, wherein the struvite,potassium struvite, or hydroxyapatite is removed from the recoverystream and used as a fertilizer.
 6. The process of claim 1, wherein theat least one cation exchange membrane comprises a polymer containinganionic groups including sulfonic and/or carboxylic groups.
 7. Theprocess of claim 1, wherein the anion exchange membrane comprises apolymer containing quaternary or tertiary amine groups.
 8. The processof claim 1, wherein the manure medium is mechanically pretreated toremove any unwanted material, larger solids and excess liquids, whereinthe pretreating is selected from screw press, centrifuge, vibratingscreen, mesh screening, belt filter or hydrocylcone.
 10. The process ofclaim 1, wherein the treated manure medium is dehydrated to minimizewater content thereby forming a solid fertilizer.
 11. A system forprecipitating struvite, potassium struvite and or hydroxyapatite, thesystem comprising: a waste compartment and a recovery compartmentpositioned within the waste compartment, wherein the recoverycompartment comprises at least one cation exchange membrane and at leastone anion exchange membrane, wherein the at least one cation exchangemembrane and the at least one anion exchange membrane are positioned onopposite or adjacent sides on the recovery compartment, and wherein therecovery compartment comprises an inlet and outlet for moving a recoverystream therethrough, and wherein the recovery stream comprising an ionicsolution comprising salts of Na⁺, K⁺, and/or NH₄ ⁺ with Cl⁻, HO⁻, HCO₃⁻, and/or HCOO⁻.
 12. The system of claim 11, wherein the cationicexchange membrane comprises a polymer containing anionic groupsincluding sulfonic and/or carboxylic groups.
 13. The system of claim 11,wherein the anion exchange membrane comprises a polymer containingquaternary or tertiary amine groups.
 14. A method to isolate struvite,potassium struvite and hydroxyapatite from a manure medium, the methodcomprising: a) providing a manure medium comprising P(V), Mg²⁺, Ca²⁺,NH₄ ⁺, and K⁺ ions; b) introducing the manure medium into a recoverysystem comprising: a waste compartment and a recovery compartmentpositioned within the waste compartment, wherein the recoverycompartment comprises at least one cation exchange membrane and at leastone anion exchange membrane, wherein the at least one cation exchangemembrane and the at least one anion exchange membrane are positioned onopposite or adjacent sides on the recovery compartment, and wherein therecovery compartment comprises an inlet and outlet for moving a recoverystream therethrough; (c) moving the manure medium into the wastecompartment, wherein the manure medium contacts both the at least onecation exchange membrane and the at least one anion exchange membrane;and (d) introducing a ionic solution comprising salts of Na⁺ or, K⁺ withCl⁻, HO⁻, HCO₃ ⁻, and/or HCOO⁻ into the recovery stream, wherein theHPO₄ ²⁻ anions in the manure medium will pass through the at least oneanion exchange membrane into the recovery stream and Mg²⁺ and NH₄ ⁺cations in the manure medium will pass through the at least one cationexchange membrane into the recovery stream, wherein a substantiallyequal amount of Na⁺ cations and Cl⁻ anions from the recovery stream willmove into manure medium, and wherein ions in the recovery stream form astruvite, potassium struvite or hydroxyapatite precipitate therebyreestablishing an electrochemical potential gradient across the at leastone cation and at least one anion exchange membrane to provide foradditional movement of ions through the at least one anion and the atleast one cation exchange membranes.
 15. The method of claim 14, wherein the struvite, potassium struvite or hydroxyapatite is removed fromthe recovery stream by a separation method.
 16. The method of claim 14,wherein the recovery stream has a pH ranging from about 7 to
 11. 17. Themethod of claim 14, wherein the cationic exchange membrane comprises apolymer containing anionic groups including sulfonic and/or carboxylicgroups.
 18. The method of claim 14, wherein the anion exchange membranecomprises a polymer containing quaternary or tertiary amine groups. 19.The method of claim 14, wherein the manure medium is mechanicallypretreated to remove any unwanted material, larger solids and excessliquids, wherein the pretreating is selected from screw press,centrifuge, vibrating screen, mesh screening, belt filter orhydrocylcone.
 20. A process for treating manure in order to isolate atleast one target precipitate, the process comprising: providing a manuremedium; introducing the manure medium into a recovery system comprising:a first and second waste compartment and a recovery compartmentpositioned between the first and second waste compartments, wherein thefirst and second waste compartments comprise an inlet and outlet formoving a first and second waste stream therethrough, respectively,wherein the recovery compartment comprises an inlet and outlet formoving a recovery stream therethrough, and wherein the first wastecompartment is separated from the recovery compartment by at least onecation exchange membrane and the second waste compartment is separatedfrom the recovery compartment by at least one anion exchange membrane;separating the manure medium into the first and second waste streams forintroducing into the inlet of the first and second waste compartments,respectively; introducing an ionic solution comprising salts of Na⁺, K⁺,and/or NH₄ ⁺ with Cl⁻, HO⁻, HCO₃ ⁻, and/or HCOO⁻ into the recoverystream, wherein anions in the first waste stream will pass through theat least one anion exchange membrane into the recovery stream andcations in the second waste stream will pass through the at least onecation exchange membrane into the recovery stream, wherein asubstantially equal amount of cations and anions from the recoverystream will move into the respective first and second waste stream, andwherein ions in the recovery stream form a precipitate comprisingstruvite, potassium struvite and/or hydroxyapatite therebyreestablishing an electrochemical potential gradient across the at leastone cation and at least one anion exchange membranes to provide foradditional movement of ions through the anion and cation exchangemembranes thereby forming additional precipitate.